Research On Influence And Suppression Algorithm Of Polarization Dependence In Distributed Optical Fiber Vibration Sensing System

Distributed optical fiber vibration sensing(DOFVS)technology represented by phasesensitive optical time domain reflectometer(?-OTDR)and polarization-sensitive optical time domain reflectometer(P-OTDR)has been used in large facility health monitoring and key facility perimeters Security,pipeline protection,marine engineering and other fields show important application value and prospects.However,the DOFVS system has problems in engineering application,such as large positioning drift,difficult multi-point vibration monitoring,high false alarm rate in harsh environments,and poor real-time data processing algorithms.Polarization correlation is one of the main factors that cause the deterioration of the performance of the DOFVS system.In this paper,three solutions are proposed for the engineering application problems caused by the polarization dependence of the system.The feasibility of the solution is verified by establishing simulation and experimental systems.Firstly,the concepts of sensing photon ‘sensing state' and ‘energy level fission' are defined,the expression of sensing photon state function considering polarization state correlation is given,the quantum sensing model of DOFVS system is established,and the quantum interpretation of sensing principle of the DOFVS system is given.The optical transmission matrix model of DOFVS system considering polarization state is established,and the output signal expression of differential interference DOFVS system considering polarization state is derived.The relationship between the power transmission coefficient of the system and the delay optical fiber,the sensing optical fiber,the interference phase difference of the light wave and the polarization angle of the incident light is analyzed by simulation,and the measures to suppress the polarization fading phenomenon in the DOFVS system are proposed.Next,a vibration location approximation algorithm based on joint Kalman filtering and information fusion is proposed.The causes of random drift of polarization-dependent vibration sensing pulses are analyzed,and the random drift model is established.The experiment studies the pre-positioning results based on the spatial drift feature and the amplitude-moment feature,and the positioning approximation result after filtering and fusing the two features.The results show that the proposed algorithm can achieve an average positioning dispersion of less than0.65 m and a maximum positioning dispersion of less than 2.2m within a response time of 80 ms.Compared with the moving average and wavelet denoising methods,the average and maximum positioning dispersion are reduced 75% and 83%.Then,a P-OTDR multi-point vibration positioning algorithm based on harmonic accumulation is proposed.The relationship between the frequency of the vibration sensing signal and each vibration frequency is derived,which proves the feasibility of using harmonic accumulation to achieve multi-point vibration positioning.The simulation model of the system is established,and the performance of the algorithm is verified by simulation and experiment.The results show that the algorithm can solve the problem of superimposed crosstalk of multivibration events,realize multi-point vibration detection,and avoid the problem of underreporting of traditional spectral analysis methods in multi-point vibration detection with different frequency.Finally,an adaptive polarization fading suppression DOFVS system and two long-distance DOFVS systems are proposed.The power cost of the system is analyzed,and it is proved that the two long-distance DOFVS systems can increase the sensing distance by 10 km.The expression of the backscatter signal in the system with and without vibration is derived,and the backscatter trace with vibration,the positioning results based on power range and standard deviation,the frequency response characteristics of the system,and the relationship between the positioning eigenvalues and the delay optical fiber are simulated and analyzed.The results show that the positioning performance of the long-distance DOFVS system based on ?-OTDR is more excellent.